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Abstract:

Hydraulic transmission apparatus including a pressurized fluid source and
at least one hydraulic motor fed by said pressurized fluid source. The
motor has two motor ducts for feed/discharge, and one casing duct. The
motor can be operated in assisted mode, in which it generates torque or
in unassisted mode in which it does not generate any torque and its
pistons are maintained in the retracted position under the effect of the
pressure in the casing duct. The apparatus further includes an
accumulator suitable for feeding: the motor ducts during a stage of
passing from the unassisted mode to the assisted mode in order to
facilitate deployment of the pistons; and the casing duct during a stage
of passing from the assisted mode to the unassisted mode in order to
facilitate retraction of the pistons.
This apparatus thus enables the motor to be positively
clutched/declutched quickly.

Claims:

1. Hydraulic transmission apparatus for a vehicle, the apparatus
including a pressurized fluid source and at least one hydraulic motor
suitable for being fed with hydraulic fluid by the pressurized fluid
source in order to drive at least one vehicle mover member; the motor
being connected to: a motor duct for feeding said motor with fluid, and a
motor duct for discharging fluid from said motor, which motor ducts are
suitable for being put into communication with cylinders arranged in a
cylinder block and including pistons suitable for sliding in said
cylinders; and a casing duct connected to an internal space arranged
inside a casing containing the cylinder block; the motor being suitable
for being operated in assisted mode, in which it generates drive torque
or braking torque under the effect of a pressure difference between the
motor ducts, and in "freewheel" mode or unassisted mode in which the
motor does not generate any torque and the pistons are maintained in the
retracted position inside the cylinders; the apparatus further including
an accumulator suitable for feeding both of the motor ducts during a
stage of passing from the unassisted mode to the assisted mode in order
to facilitate deployment of the pistons; wherein the accumulator is also
suitable for feeding the casing duct so as to put said duct under
pressure during a stage of passing from the assisted mode to the
unassisted mode in order to facilitate retraction of the pistons.

2. Apparatus according to claim 1, further including an accumulator valve
that has a port connected to the accumulator, and that has a first
position in which it connects said accumulator to a filling fluid source,
and a second position in which it isolates said accumulator from said
filling fluid source.

3. Apparatus according to claim 1, including a pressurization pump
suitable for being connected to the accumulator while said motor ducts
are being put under pressure.

4. Apparatus according to claim 1, wherein said pressurized fluid source
is a main pump, and the apparatus further includes an auxiliary pump that
serves to maintain some minimum fluid pressure in at least one auxiliary
duct; the main pump and the auxiliary pump are suitable for being
actuated jointly by drive means; and the assistance apparatus further
includes: a "bypass" connection between a delivery orifice of the
auxiliary pump and an unpressurized reservoir; first constriction means
arranged on the bypass connection and suitable for maintaining a pump
protection pressure in a pump protection portion of the bypass
connection; and means for applying said pump protection pressure to main
orifices of the main pump when said pump is actuated but is not
delivering.

5. Apparatus according to claim 4, wherein the main pump is a rotary
pump, and in particular a pump having a swashplate and axial pistons.

6. Apparatus according to claim 4, wherein the first constriction means
are arranged to maintain a pump protection pressure less than 20 bars,
and preferably less than 10 bars.

7. Apparatus according to claim 4, the drive means of which comprise an
internal combustion engine having a power outlet to which the main and
auxiliary pumps are coupled continuously, i.e. without any clutches.

8. Apparatus according to claim 4, further including an accumulator valve
that has a port connected to the accumulator, and that has a first
position in which it connects said accumulator to a filling fluid source,
and a second position in which it isolates said accumulator from said
filling fluid source, and including a bypass valve interposed on said
bypass connection and having: a first position, in which said bypass
valve enables the auxiliary pump to deliver through the bypass
connection; and a second position, in which said bypass valve interrupts
the flow through said bypass connection and enables fluid to pass towards
said at least one auxiliary duct; and in addition, the bypass valve and
the accumulator valve are coupled together, i.e. when the bypass valve is
in the first position, the accumulator valve is in the first position,
and when the bypass valve is in the second position, the accumulator
valve is in the second position.

9. Apparatus according to claim 8, wherein the accumulator valve has a
hydraulic control chamber that is connected to a port of the bypass valve
enabling the accumulator valve to be controlled by the bypass valve.

10. Apparatus according to claim 4, including second constriction means
arranged on the bypass connection, and suitable for maintaining a motor
protection pressure in a motor protection portion of the bypass
connection; and wherein said motor protection portion is suitable for
being connected to said casing duct.

11. Apparatus according to claim 10, wherein the first constriction means
include a first calibrated valve, calibrated to the pump protection
pressure, and the second constriction means include a second calibrated
valve, calibrated to the motor protection pressure, said first calibrated
valve and said second calibrated valve being arranged in series on the
bypass connection.

12. Apparatus according to claim 1, wherein: said pressurized fluid
source is a main pump; the apparatus further includes an auxiliary pump
serving to maintain some minimum fluid pressure in at least one auxiliary
duct; the apparatus includes two pump ducts connected to the main
orifices of the main pump, and an activation valve having two upstream
ports suitable for being connected to the two pump ducts, and two
downstream ports suitable for being connected to the two motor ducts; and
said activation valve has a first position in which the two upstream
ports are interconnected, and the two downstream ports are
interconnected, and a second position in which the two upstream ports are
connected to respective ones of the two downstream ports.

13. Apparatus according to claim 12, wherein the activation valve further
includes a third upstream port suitable for being connected to the
accumulator and/or to the auxiliary pump; when the activation valve is in
the first position, the third upstream port is connected to the two
downstream ports and is thus suitable for being connected to the two
motor ducts; when the activation valve is in the second position, the
third upstream port is isolated.

14. Apparatus according to claim 12, wherein said pressurized fluid
source is a main pump, and the apparatus further includes an auxiliary
pump that serves to maintain some minimum fluid pressure in at least one
auxiliary duct; the main pump and the auxiliary pump are suitable for
being actuated jointly by drive means; and the assistance apparatus
further includes: a "bypass" connection between a delivery orifice of the
auxiliary pump and an unpressurized reservoir; first constriction means
arranged on the bypass connection and suitable for maintaining a pump
protection pressure in a pump protection portion of the bypass
connection; and means for applying said pump protection pressure to main
orifices of the main pump when said pump is actuated but is not
delivering; said apparatus further including an accumulator valve that
has a port connected to the accumulator, and that has a first position in
which it connects said accumulator to a filling fluid source, and a
second position in which it isolates said accumulator from said filling
fluid source, and including a bypass valve interposed on said bypass
connection and having: a first position, in which said bypass valve
enables the auxiliary pump to deliver through the bypass connection; and
a second position, in which said bypass valve interrupts the flow through
said bypass connection and enables fluid to pass towards said at least
one auxiliary duct; and in addition, the bypass valve and the accumulator
valve are coupled together, i.e. when the bypass valve is in the first
position, the accumulator valve is in the first position, and when the
bypass valve is in the second position, the accumulator valve is in the
second position; and including a pilot valve having an outlet port
connected to a hydraulic control chamber controlling the position of the
activation valve, and an inlet port that is suitable for being connected
to a pilot fluid source via said bypass valve, and said pilot valve is
suitable for putting said pilot fluid source and said control chamber
into communication with each other or for isolating them from each other.

15. A transmission system for a vehicle, including a main transmission
suitable for driving vehicle mover members, and an auxiliary transmission
including apparatus according to claim 1.

Description:

FIELD OF THE INVENTION

[0001] The invention relates to hydraulic transmission apparatus for a
vehicle, the apparatus including a pressurized fluid source and at least
one hydraulic motor suitable for being fed with hydraulic fluid by the
pressurized fluid source in order to drive at least one vehicle mover
member;

[0002] the motor being connected to:

[0003] a motor duct for feeding said motor with fluid, and a motor duct
for discharging fluid from said motor, which motor ducts are suitable for
being put into communication with cylinders arranged in a cylinder block
and including pistons suitable for sliding in said cylinders; and

[0005] the motor being suitable for being operated in assisted mode, in
which it generates drive torque or braking torque under the effect of a
pressure difference between the motor ducts, and in "freewheel" mode or
unassisted mode in which the motor does not generate any torque and the
pistons are maintained in the retracted position inside the cylinders;

[0006] the apparatus further including an accumulator suitable for feeding
both of the motor ducts during a stage of passing from the unassisted
mode to the assisted mode in order to facilitate deployment of the
pistons.

[0007] In unassisted mode, the motor is positively declutched; the pistons
are maintained in the retracted position under the effect of the pressure
prevailing in the internal space connected to the casing duct. Mechanical
means such as springs or the like can be used in addition to the fluid
pressure for making it easier to maintain the pistons in the retracted
position.

BACKGROUND OF THE INVENTION

[0008] Such apparatus is, in particular, used in assistance on a vehicle,
so as to make it possible, whenever necessary, to actuate the hydraulic
motor as a supplementary or assistance motor, for moving the vehicle
under difficult movement conditions, such as slippery ground, steep
slope, etc. Typically, the hydraulic motor is arranged on an axle of the
vehicle that is an axle on which the wheels are not driven wheels when
the vehicle is in normal advance mode; thus, when the hydraulic
transmission apparatus is activated, the vehicle has additional driven
wheels.

[0009] A particularly important application of the invention relates to
hydraulic assistance apparatus mounted on road vehicles such as heavy
goods vehicles that can travel at some speed (over 50 kilometers per hour
(km/h)). For such an application, the hydraulic assistance apparatus must
satisfy certain additional constraints: firstly, it must guarantee full
safety when the vehicle is traveling at high speeds, i.e. it must be
almost impossible for the assistance motors to be triggered in untimely
manner; secondly the apparatus must make it possible for the assistance
motors to be switched on while the vehicle is advancing, and not merely
when it is at a standstill or while it is traveling at very low speed
(less than 5 km/h).

[0010] The accumulator is a hydraulic accumulator of the rechargeable
spring or gas type that contains pressurized fluid and is capable of
storing hydraulic energy in the form of hydrostatic energy and of
delivering hydraulic energy using the stored hydrostatic energy.

[0011] In order to enable the hydraulic transmission apparatus to be
relatively practical to use, it is necessary for it to be quite simple
and quick to activate or to deactivate.

[0012] This constraint is particularly important when the assistance motor
is a motor of the positively declutchable type that has radial pistons
arranged to act on an undulating cam, it being possible for said radial
pistons to be retracted into the cylinders in such manner as to enable
the motor to be positively declutched. In such a motor, the need for
rapid switch-over from unassisted mode to assisted mode and vice versa
does not only concern the ergonomics of the apparatus; quick positive
clutching/declutching of the motor is also necessary in order to avoid
damaging the motor during positive clutching or declutching, by limiting
any rattling and jolting that is caused by such operations.

[0013] In order to facilitate positive clutching of the motor, it is
possible, in known manner, to use an accumulator. An accumulator
constitutes a supplementary pressurized fluid source; the pressure that
it delivers can be transmitted to the motor ducts in order to accelerate
deployment of the pistons out of the cylinders, and thus in order to
accelerate positive clutching.

OBJECT AND SUMMARY OF THE INVENTION

[0014] An object of the invention is to provide transmission apparatus of
the type described in the introduction, and in which not only can
positive clutching be performed quickly, but also the time taken by
positive declutching is reduced, in order to protect the motor during
this stage and in order to procure a system that is quick to activate and
to deactivate.

[0015] This object is achieved by means of the fact that the accumulator
is also suitable for feeding the casing duct so as to put said duct under
pressure during a stage of passing from the assisted mode to the
unassisted mode in order to facilitate retraction of the pistons. During
this stage, the accumulator puts the casing duct at a pressure greater
than the pressure of the motor ducts, in order to ensure that the
pressure differential in the cylinders across the pistons is established
in the direction that facilitates retraction of the pistons.

[0016] By means of the pressure imposed by the accumulator, the positive
declutching is accelerated, thereby increasing the flexibility of use of
the vehicle. The use of the accumulator for facilitating both deployment
and retraction of the pistons makes it possible to avoid using a large
booster pump, which would add considerably to the cost of the apparatus.

[0017] In an embodiment, the apparatus is advantageously arranged in such
a manner as to enable the accumulator to be emptied via a constriction,
and the accumulator is put into communication with the casing duct so as
to make it possible for the pistons to be retracted during the emptying
stage itself (i.e. while the fluid that the accumulator contains is being
removed towards an unpressurized reservoir). Naturally, in this situation
the connection between the casing duct and the accumulator is on the
accumulator side of the constriction.

[0018] Due to the constriction, emptying the accumulator requires a
certain length of time, during which the pressure in the vicinity of the
accumulator firstly remains relatively high, before decreasing
progressively. By means of this, putting the accumulator and the casing
duct into communication with each other for facilitating retraction of
the pistons can take place during the operation of emptying the
accumulator.

[0019] In addition, the use of an accumulator can suffer from certain
risks, in particular if the accumulator remains under pressure while the
vehicle is being used, and more particularly for long periods and in
unassisted mode, on the road.

[0020] In order to reduce this risk, in a preferred embodiment, the
apparatus further includes an accumulator valve that has a port connected
to the accumulator, and that has a first position in which it connects
(or is suitable for connecting) said accumulator to a filling fluid
source, and a second position in which it isolates said accumulator from
said filling fluid source.

[0021] The accumulator valve procures considerable flexibility in managing
the accumulator, in particular with a view to putting said accumulator
under pressure only for the time for which it is necessary. The
accumulator is then connected to the filling fluid source for a
sufficient length of time, preferably just before its use stage. This
applies, in particular at the time of passing to assisted mode, during
which time the pressure of the accumulator is used to facilitate and to
accelerate deployment of the pistons out of the cylinders. Conversely,
while the vehicle is traveling at high speed or is at a standstill, the
accumulator can remain empty.

[0022] In an embodiment, the apparatus includes a pressurization pump
suitable for being connected to the accumulator while said motor ducts
are being put under pressure. As a result, during the stage of putting
the motor ducts under pressure, the motor ducts are then connected both
to the above-indicated pump and to the accumulator. This makes it
possible to accelerate filling the motor ducts with fluid and putting
them under pressure on passing to assisted mode.

[0023] In addition, in general, in assistance apparatus such as the
apparatus of the invention, since the assistance apparatus is used only
occasionally, the problem arises of activating the hydraulic transmission
apparatus: the means devoted to activation and deactivation must be
relatively limited, and proportionate to the function of the apparatus,
which is not more than providing assistance.

[0024] The solution usually chosen consists in providing a clutch system
interposed between the internal combustion engine of the vehicle or of
the machine and the main pump of the apparatus. Such a clutch system is
quite costly, occupies a large volume, and requires a considerable amount
of maintenance.

[0025] More particularly, an embodiment of such a solution is known for
hydraulic transmission apparatus including a positively declutchable
radial-piston hydraulic motor similar to the motor used in the apparatus
of the invention.

[0026] In such apparatus, it is useful at all times to have at least some
minimum pressure that can be applied to the insides of the internal
spaces of the motors and thus that can maintain said motors in the
positively declutched positions, with their pistons retracted into their
cylinders. The technical solution adopted in such apparatus consists in
making provision not only for the main pump to be declutchable by means
of a clutch, but also for the internal combustion engine to actuate an
auxiliary pump or booster pump of the apparatus continuously, so that
fluid under some minimum pressure is delivered continuously, thereby
guaranteeing that the assistance motors are maintained in positions in
which they are positively declutched and thus safe.

[0027] Thus, in unassisted mode, since the main pump is declutched, there
is no risk of it being damaged under the effect of insufficient pressure
at its main orifices.

[0028] That technical solution still suffers from the drawback of using a
clutch, but it does procure a certain amount of safety for the use of the
positively declutchable hydraulic motors. However, the auxiliary pump
operating continuously gives rise to non-negligible power consumption. In
addition, the internal combustion engine has to have two outlets, one
towards the clutch connected to the main pump, and the other towards the
auxiliary pump. This gives rise to compactness problems, and requires the
internal combustion engine to have a specific and complex design.

[0029] In order to remedy those drawbacks, a specific embodiment of the
invention is proposed. This embodiment concerns the situation wherein the
pressurized fluid source is a main pump, and the apparatus further
includes an auxiliary pump that serves to maintain some minimum fluid
pressure in at least one auxiliary duct, and wherein the main pump and
the auxiliary pump are suitable for being actuated jointly by drive
means.

[0030] Such drive means may be of any type, but in general they are
constituted by an internal combustion engine, e.g. a diesel engine. A
diesel engine is used in the following description in order to facilitate
understanding. However, the description remains applicable regardless of
the drive means actuating the pumps of the apparatus.

[0031] In such assistance apparatus, in known manner, the main pump may be
a hydraulic pump having a variable delivery rate, thereby making it
possible to adapt the speed of the motors as a function of need.

[0032] The specific embodiment proposed concerns hydraulic assistance
apparatus including such a pump as the main pump, and more generally such
apparatus in which the main pump is a pump that can be actuated without
delivering, but that then requires some minimum pressure to be applied to
its main orifices. If such pumps are actuated while pressure lower than
the above-mentioned minimum pressure prevails in either of the main
orifices of the pump, a risk of damaging the pump ensues.

[0033] In order to remove that risk, in the specific embodiment proposed,
the assistance apparatus further includes: [0034] a "bypass" connection
between a delivery orifice of the auxiliary pump and an unpressurized
reservoir; [0035] first constriction means arranged on the bypass
connection and suitable for maintaining a pump protection pressure in a
pump protection portion of the bypass connection; and [0036] means for
applying said pump protection pressure to main orifices of the main pump
when said pump is actuated but is not delivering.

[0037] Advantageously, this arrangement makes it possible to operate the
apparatus in an unassisted mode in which the above-mentioned risk is
removed; power consumption is low; and this result is then obtained even
though the apparatus does not include any clutch.

[0038] In unassisted mode, the main and auxiliary pumps are actuated
continuously. However, the main pump is then not delivering, and so its
power consumption remains tiny; in addition the consumption of the
auxiliary pump also remains tiny, because the pressure at its delivery
orifice is set at a relatively low pressure level that is merely
sufficient to protect the main pump. Finally, the main pump is protected
because a "pump protection pressure" is applied to its main orifices
during the unassisted mode, this pressure naturally being chosen to be
sufficient to guarantee that the pump is protected (but also to be as low
as possible).

[0039] In an embodiment, the main pump is a rotary pump, and in particular
a pump having a swashplate and axial pistons.

[0040] In an embodiment, the first constriction means are arranged to
maintain a pump protection pressure less than 20 bars, and preferably
less than 10 bars. By means of these particularly low pressures, the
auxiliary pump in unassisted mode consumes little power even though it is
being actuated. The pump protection pressure is at least the pressure
that it suffices to apply to the main orifices of the main pump in order
to enable said main pump to operate without being damaged.

[0041] In an embodiment, the drive means comprise an internal combustion
engine having a power outlet to which the main and auxiliary pumps are
coupled continuously, i.e. without any clutches.

[0042] In an embodiment, the apparatus includes a bypass valve interposed
on said bypass connection and having:

[0043] a first position, in which said bypass valve enables the auxiliary
pump to deliver through the bypass connection; and

[0044] a second position, in which said bypass valve interrupts the flow
through said bypass connection and enables fluid to pass towards said at
least one auxiliary duct. This feature makes it possible to use the
bypass valve as a trigger element for switching over between the assisted
and the unassisted modes.

[0045] The bypass valve is then a general activation/deactivation valve
for the assistance circuit.

[0046] It thus firstly has a first position corresponding to the
unassisted mode of the apparatus, in which position minimum functions are
ensured by the apparatus, in particular by means of the fact that the
boost pressure (pressure at the delivery orifice of the auxiliary pump)
or a pressure dependent on the boost pressure can be applied at different
sensitive points of the apparatus, in particular the internal spaces of
the above-mentioned motor, so as to guarantee that the motor is
maintained in the positively declutched position.

[0047] The bypass valve also has a second position, corresponding to the
assisted mode of the apparatus, in which position the booster pump is
suitable for delivering pressurized fluid to various members of the
apparatus via auxiliary ducts, in particular to the motors so as to
facilitate positive clutching of the pistons (deployment of the pistons
out of their cylinders).

[0048] When an accumulator valve is disposed on the filling and emptying
line for filling and emptying the accumulator, and in one embodiment, the
bypass valve and the accumulator valve are coupled together, i.e. when
the bypass valve is in the first position, the accumulator valve is in
the first position, and when the bypass valve is in the second position,
the accumulator valve is in the second position.

[0049] The advantage of this arrangement is that it makes it possible,
when the bypass valve is in the first position, to put the accumulator
and the auxiliary duct under pressure, and thus to use the accumulator in
assisted mode. Conversely, in the second position, use of the accumulator
is not possible, and is therefore disabled in unassisted mode, thereby
procuring safety in use of the apparatus.

[0050] It should be noted that this embodiment of hydraulic transmission
apparatus may also be implemented in apparatus differing from apparatus
of the invention merely by the fact that in such differing apparatus the
accumulator is not provided for feeding the casing duct in order to put
said casing duct at a pressure greater than the pressure in the motor
ducts, during a stage of switching over from the assisted mode to the
unassisted mode, in order to facilitate retraction of the pistons.

[0051] In an embodiment, in order to perform the coupling between the
bypass valve and the accumulator, the accumulator valve has a hydraulic
control chamber that is connected to a port of the bypass valve enabling
the accumulator valve to be controlled by the bypass valve. Thus, the
bypass valve is suitable for placing the accumulator in "pressurized"
mode (the accumulator being connected to the auxiliary or booster pump)
during the assisted mode, and for leaving the accumulator at zero
pressure during the unassisted mode.

[0052] In an embodiment, the apparatus includes second constriction means
arranged on the bypass connection, and suitable for maintaining a motor
protection pressure in a motor protection portion of the bypass
connection; and the motor protection portion (of the bypass connection)
is suitable for being connected to said casing duct.

[0053] This feature is provided for the unassisted mode. In this mode, the
fluid delivered by the auxiliary pump flows through the bypass
connection. Under these conditions, the second constriction means
maintain a "motor protection" pressure in a "pump protection connection"
portion of said connection, which pressure is in general much lower than
the pump protection pressure, and is sufficient to protect the motor(s).
For example, for positively declutchable motors such as the
above-described motors, the motor protection pressure is merely the
pressure sufficient to maintain the pistons in the retracted position
inside the cylinders, i.e. about 0.5 bars usually.

[0054] In an embodiment, the first constriction means include a first
calibrated valve, calibrated to the pump protection pressure, and the
second constriction means include a second calibrated valve, calibrated
to the motor protection pressure, said first calibrated valve and said
second calibrated valve being arranged in series on the bypass
connection.

[0055] In an embodiment:

[0056] said pressurized fluid source is a main pump;

[0057] the apparatus further includes an auxiliary pump serving to
maintain some minimum fluid pressure in at least one auxiliary duct;

[0058] the apparatus includes two pump ducts connected to the main
orifices of the main pump, and an activation valve having two upstream
ports suitable for being connected to the two pump ducts, and two
downstream ports suitable for being connected to the two motor ducts; and

[0059] said activation valve has a first position in which the two
upstream ports are interconnected, and the two downstream ports are
interconnected, and a second position in which the two upstream ports are
connected to respective ones of the two downstream ports.

[0060] The activation valve is the valve that feeds the assistance
motor(s) when they are activated, when it is in the second position, or
isolates them from the pump ducts, when it is in the first position.

[0061] In an embodiment, the activation valve further includes a third
upstream port suitable for being connected to the accumulator and/or to
the auxiliary pump; when the activation valve is in the first position,
the third upstream port is connected to the two downstream ports and is
thus suitable for being connected to the two motor ducts; when the
activation valve is in the second position, the third upstream port is
isolated.

[0062] The connection established between the third upstream port and a
pressurized fluid source thus makes it possible to impose a pressure in
the motor ducts (e.g. a pressure dependent on the delivery pressure of
the auxiliary pump), which is particularly effective for facilitating
deployment or retraction of the pistons relative to the cylinders of the
motor.

[0063] This connection may, in particular, be used for filling and
emptying of the motor ducts.

[0064] In an embodiment, the apparatus includes a pilot valve having an
outlet port connected to a hydraulic control chamber controlling the
position of the activation valve, and an inlet port that is suitable for
being connected to a pilot fluid source via said bypass valve, and said
pilot valve is suitable for putting said pilot fluid source and said
control chamber into communication with each other or for isolating them
from each other.

[0065] This arrangement offers the advantage of thus having the bypass
valve and the first pilot valve in series, in the control line of the
activation valve. Since it is necessary for two valves to be in specific
positions in order to enable the pilot valve to be activated, the risk of
accidental failure and thus of untimely and undesired activation of the
assistance motor is reduced to the minimum. Naturally, the bypass and
pilot valves should be arranged so that their respective default
positions correspond to the positions in which no instruction for going
into a second position or activation position is transmitted to the
activation valve.

[0066] An object of the invention is also to provide a transmission system
for a vehicle, including a main transmission suitable for driving vehicle
mover members, and an auxiliary transmission making it possible to
deliver supplementary drive torque when circumstances so require, which
system has relatively low power consumption, and has its auxiliary
transmission implemented simply and in a manner requiring little
maintenance.

[0067] This object is achieved by means of the fact that the auxiliary
transmission is constituted by apparatus as defined above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0068] The invention can be well understood and its advantages appear more
clearly on reading the following detailed description of an embodiment
shown by way of non-limiting example. The description refers to the
accompanying drawings, in which:

[0069] FIG. 1 is a generic diagram of a vehicle on which apparatus of the
invention is mounted;

[0070]FIG. 2 is a timing diagram showing the various stages in
implementing the apparatus of FIG. 1, as a function of time;

[0071] FIGS. 3 to 5 are diagrams showing the apparatus of FIG. 1 in
unassisted mode:

[0072]FIG. 3 is a diagram showing the apparatus of FIG. 1 in freewheel
mode and during the step of retracting the pistons;

[0073]FIG. 4 is a diagram showing the apparatus of FIG. 1, during the
step of deploying the pistons; and

[0074] FIG. 5 is a diagram showing the apparatus of FIG. 1, in assisted
mode; and

[0075] FIGS. 6A and 6B are diagrammatic axial section views of the
activation valve of the apparatus of FIG. 1.

MODE DETAILED DESCRIPTION

[0076] FIG. 1 shows a vehicle 10 on which apparatus 20 of the invention is
mounted.

[0077] The vehicle 10 is a vehicle having four wheels, namely two rear
wheels 12A & 12B and two front wheels 14A & 14B. The drive for the
vehicle is delivered mainly by a main transmission 16. Said main
transmission includes a diesel engine 18 ("drive means" in the meaning of
the invention) that is connected to the rear wheels 12A & 12B and that
drives the vehicle in a normal advance mode of said vehicle.

[0078] In addition, in order to ensure that the vehicle is propelled even
under difficult road conditions (sloping or downhill road, slippery road,
etc.), the vehicle also has an auxiliary transmission 20. Said auxiliary
transmission serves to drive the two wheels 14A and 14B that are not
driven wheels while the vehicle is in normal advance mode. Thus, by means
of the auxiliary transmission 20, the vehicle has an assisted mode in
which all four wheels 12A, 12B, 14A and 14B are driven wheels.

[0079] The auxiliary transmission 20 is coupled to a shaft 21 that is the
power outlet of the engine 18, from which it takes the power that it
transmits to the wheels 14A & 14B when it is activated.

[0080] The auxiliary transmission 20 is constituted by hydraulic
transmission apparatus 22 that transmits a fraction of the power from the
engine 18 to the wheels 14A & 14B, and that also performs various
additional functions: activation/deactivation of the auxiliary
transmission, making the members of the auxiliary transmission safe
during the deactivated mode, etc.

[0081] For driving the wheels 14A, 14B, the hydraulic transmission
apparatus 22 firstly includes two pressurized fluid sources: a main pump
24, and an auxiliary pump 25 for maintaining some minimum fluid pressure
in various auxiliary ducts of the apparatus.

[0082] The main pump 24 is a reversible pump having a variable delivery
rate and a swashplate.

[0083] Both the main pump 24 and the auxiliary pump 25 are connected to
the outlet shaft 21 of the engine 18 directly, i.e. without any clutches.
They can thus be actuated jointly by the engine 18, i.e. both pumps can
be driven at the same time.

[0084] The main pump 24 serves to feed pressurized fluid to two hydraulic
motors 26A, 26B that are coupled to respective ones of the two wheels
14A, 14B. For this purpose, the pump 24 has two pump ducts 28A, 28B
connected to respective ones of its main orifices 24A, 24B.

[0085] Said orifices can be put into communication with respective ones of
two motor ducts 30, 32. Each of said motor ducts has a first portion 301,
321 suitable for being connected to a pump duct, and a second portion in
which it splits into two branches 302A, 302B, 322A, 322B connected to
respective ones of feed and discharge enclosures of the motors 26A and
26B.

[0086] In a manner known per se, the motors 26A, 26B are hydraulic motors
having radial pistons, each of which motors comprises a cylinder block in
which cylinders are arranged that contain pistons. The pistons can be
positively declutched to take up a retracted position in which they are
retracted into the cylinders and in which they do not deliver any torque,
or they can be positively clutched to take up a deployed position, in
which they (partially) extend from the cylinders and come to bear on an
undulating cam that transforms their radial forces into drive torque.
Such motors are, for example, described in French Patent No. 2 504 987.

[0087] Each of the motors 26A, 26B has an outlet shaft coupled to a
respective one of wheels 14A & 14B. Under the effect of the pressure
difference imposed by the main pump between the pump ducts, and thus
between the motor ducts, in assisted mode, the motors 26A and 26B deliver
drive torque (or braking torque) that enables them to drive the wheels
14A & 14B.

[0088] An activation valve 34 is interposed between the pump ducts 28A,
28B and the motor ducts 30, 32. Said activation valve has four "upstream"
ports A, B, C, D, two "downstream" ports E and F, two positions I & II,
and two hydraulic control chambers 34A & 34B. In this text the terms
"upstream" and "downstream" as applied to the ports of a valve designate,
in general, the most frequent direction of flow of the fluid, or of
transmission of an instruction, without this excluding other operating
modes.

[0089] Ports A and D are connected to pump duct 28A. Port C is connected
to pump duct 28B. Ports E and F are connected to motor ducts 30 and 32.
Port B is connected to a pressure control valve 36.

[0090] The activation valve 34 also has a return spring that tends to
maintain it in its first position I.

[0091] In the first position I, port A is isolated, port B is connected to
ports E and F, and ports C and D are interconnected.

[0092] In the second position II, ports B and D are isolated, ports A & E
are interconnected and ports C & F are interconnected (ports A & D remain
interconnected and connected to pump duct 28A).

[0093] Thus, in the first position I, pump ducts 28A & 28B are
interconnected (bypass position); the pump is then set to a delivery rate
of zero. In addition, the motor ducts are interconnected, and their
pressure is the pressure that is imposed on them by the pressure control
valve 36, in a manner described below.

[0094] Conversely, in the second position II, the motor ducts are
connected to the pump ducts and they feed the motors 26A & 26B so that
they drive the wheels 14A & 14B, which constitutes the assisted mode of
the apparatus.

[0095] In addition, each of the motors 26A & 26B has a casing 38A, 38B
containing its cylinder block. An internal space is provided inside the
casing, and is connected to a duct for casing duct leak return
(references 40A & 40B) connected to an unpressurized reservoir in a
manner described in detail below.

[0096] The delivery orifice of the auxiliary pump 25 is connected to a
boost duct 41.

[0097] The boost duct 41 is connected to the pump ducts 28A, 28B via
non-return or "check" valves 42A, 42B. This connection makes it possible
to ensure that the pressure in the pump ducts remains at all times at the
level of the boost pressure (pressure at the delivery orifice of the pump
25).

[0098] In addition, the duct 41 is connected to an unpressurized reservoir
46 that is at atmospheric pressure, via a pressure limiter 44 that
prevents any excessive rise in pressure in the duct 41.

[0099] Similarly, the pump ducts 28A, 28B are connected to the duct 41 via
pressure limiters 48A, 48B, also in order to avoid any excessive
pressure.

[0100] A "bypass" solenoid valve 50 is disposed on the boost duct. Said
solenoid valve has two upstream ports A and B, two downstream ports C and
D, and two positions I and II.

[0101] Port A is connected to an unpressurized reservoir 52 (which may the
same as the reservoir 46). Port B is connected to an end of the boost
duct 41. Port C is connected to a "transmission" duct 54, the purpose of
which is described in more detail below. Port D is connected to a
"bypass" duct 56.

[0102] The bypass valve 50 also has a return spring that tends to maintain
it in its first position I.

[0103] In the first position I, ports A and C are interconnected, and
ports B and D are interconnected.

[0104] In the second position II, ports A and D are interconnected, and
ports B and C are interconnected.

[0105] The first position I is a default position for the bypass valve 50
and is the "deactivated" position, corresponding to the "unassisted" mode
(normal advance mode). In this position, the fluid coming from the
booster pump is directed towards the boost duct 56, and the transmission
duct 54 is maintained at zero pressure (which, in this document, means
atmospheric pressure).

[0106] The second position II of the bypass valve is the "activated" mode
of the transmission apparatus 22, corresponding to the "assisted" mode
for the vehicle. In this second position, the bypass valve directs the
flow from the booster pump towards the transmission duct 54, which is an
auxiliary duct of the apparatus 22.

[0107] The bypass duct 56 has three portions, namely an upstream portion
561, a middle portion 562, and a downstream portion 563.

[0108] The upstream portion 561 and the middle portion 562 are
interconnected via a pressure limiter 58 and via a check,valve 60 that
are mounted in parallel. The check valve is mounted in the direction that
prevents the fluid from flowing towards the middle portion 562.

[0109] The pressure limiter 58 is controlled by its upstream pressure, and
makes it possible to maintain a minimum pressure in its upstream portion
561 that is chosen to be equal to 10 bars.

[0110] The middle portion 562 and the downstream portion 563 are
interconnected via a calibrated valve 62. Said calibrated valve
guarantees that a minimum pressure is maintained in the middle portion
that is chosen to be equal to 0.5 bars.

[0111] The boost duct 41 associated with the bypass duct 56 form a
"bypass" connection 64. Said bypass connection thus interconnects the
delivery orifice of the auxiliary pump 25 and the unpressurized reservoir
52.

[0112] As explained above, the boost duct 41 is connected to the pump
ducts 28A and 28B (via the valves 42A, 42B). Thus in assisted mode (valve
50 in position I), the pressure of 10 bars (more precisely 10.5 bars)
maintained by the pressure limiter 58 in the upstream portion of the
bypass connection (uniting the boost duct 41 and the upstream portion 561
of the bypass duct) applies in the pump ducts; as a result, the pump is
protected. The pressure maintained by the limiter 58 is thus a "pump
protection" pressure, and the upstream portion of the bypass link is thus
a "pump protection" portion.

[0113] The middle portion 562 of the bypass duct 56 is connected via a
duct 66 to the casing ducts 40A and 40B. Thus, the pressure in the casing
ducts remains at all times no more than 0.5 bars (calibration pressure of
the valve 62). However, in transient manner, the pressure can increase to
a greater extent in said middle portion 562 since the maximum flow rate
that the valve 62 can remove is relatively limited. This property is used
in the circuit in a manner that is described in detail below.

[0114] The activation valve 34 is controlled by a first pilot valve 68.

[0115] Said first pilot valve is a solenoid valve having two upstream
ports A & B, and two downstream ports C & D, and two positions I & II.

[0116] Port A is connected to the transmission duct 54. It can be
understood that said transmission duct transmits a boost pressure that
the first pilot valve 68 can use to control the activation valve. Port B
is connected to a removal duct 70 that is itself connected to the
unpressurized reservoir 52. Port C is connected to the hydraulic chamber
34B of the valve 34, the increase in the pressure of which chamber tends
to cause the activation valve 34 to go into its first position
(unassisted mode); port D is connected to the other chamber 34A of the
valve 34, the increase in the pressure of which chamber tends,
conversely, to cause the valve 34 to go into its second position
(assisted mode).

[0117] The first pilot valve 68 also has a return spring that tends to
maintain it in the first position I.

[0118] In the first position I, ports A and C are interconnected, and
ports B and D are interconnected; and, in the second position II, ports A
and D are interconnected, and ports B and C are interconnected.

[0119] Since the first pilot value 68 is situated downstream from the
bypass valve 50, it is active only when the bypass valve is in position
II, and thus only when the boost pressure is prevailing in the
transmission duct 54.

[0120] Under these conditions, action on the valve 68 makes it possible to
cause the activation valve to go into position I or into position II,
depending on whether the pilot valve is itself placed in position I or in
position II. When the first pilot valve 68 is in position I, the boost
pressure is transmitted into the chamber 34A, and zero pressure is
maintained in the chamber 34B, so that the activation valve 34 is placed
in position I (unassisted mode); and vice versa.

[0121] The apparatus 22 also has a second pilot valve 72 that controls the
pressure control valve 36.

[0122] Firstly, the arrangement of the hydraulic valve 36 is specified
below. This valve has two upstream ports A and B, one downstream port C,
and a hydraulic control chamber 361. Port C of the valve 36 is connected
to port B of the activation valve 34.

[0123] The valve 36 has two positions I and II. In the first position I,
the ports A and C are interconnected, and port B is isolated. In the
second position II, ports B and C are interconnected, and port A is
isolated.

[0124] The valve 36 also has a return spring that tends to maintain it in
the first position I.

[0125] The second pilot valve 72 is a solenoid valve having two upstream
ports A and B, and one downstream port C.

[0126] Ports A and B are connected respectively to the transmission duct
54 and to the removal duct 70. Port C is connected to the hydraulic
control chamber 361 of the pressure control valve 36.

[0127] The second pilot valve 72 also has a return spring that tends to
maintain it in the first position I.

[0128] In its first position I, the second pilot valve 72 interconnects
ports B and C, A remaining isolated. In the second position II, the
second pilot valve 72 interconnects A and C, B remaining isolated.

[0129] Like for the first pilot valve, the valves 36 and 72 are active
only during the assistance stages, i.e., in this example, when the bypass
valve 50 is placed in position II. The boost pressure then prevails in
the transmission duct 54 (connected to port A of the valve 72), while
zero pressure prevails in the removal duct 70 (connected to port B of the
valve 72).

[0130] Under these conditions, the valve 72 makes it possible to apply
either the boost pressure or a zero pressure to the hydraulic control
chamber 361 of the valve 36, depending on whether it is placed in its
first or in its second position. The pressure in the chamber 361
constrains the valve 36 to take up its first position I if the valve 72
is in its first position I, or to take up its second position if the
valve 72 is in its second position II.

[0131] This arrangement thus makes it possible to select the pressure that
it is desired to apply to port B of the activation valve 34. When said
activation valve is in its first position I, the pressure in port B is
transmitted to the motor ducts 30, 32 (conversely, when the activation
valve is in the second position II, port B is isolated).

[0132] Finally, the apparatus 22 has an additional pressurized fluid
source, namely a fluid accumulator 74, operation of which is regulated by
an accumulator valve 76, disposed on an accumulator duct that connects
the accumulator 74 to the remainder of the apparatus.

[0133] The accumulator valve 76 has an upstream port A, two downstream
ports B and C, and a hydraulic control chamber 761. Port A is connected
to the accumulator. Port B is connected to the middle portion 562 of the
bypass duct 56, via the duct 66. Port C is connected to the transmission
duct 54.

[0134] The accumulator valve 76 can take up a first position I, in which
the valves A and C are interconnected, and the port B is isolated; and a
second position II, in which the ports A and B are interconnected, and
the port C is isolated.

[0135] The accumulator valve 76 has a return spring that tends to urge it
to return to its first position I.

[0136] The control chamber 761 of the accumulator valve 76 is connected to
the upstream portion 561 of the bypass duct 56. As a result of this
connection:

[0137] If the bypass valve 50 is in position I (unassisted mode), the
boost pressure (the value of which in this mode is set at a "pump
protection" value) applies in the hydraulic chamber 761 and thus, the
accumulator valve is placed in position II, in which the accumulator is
connected to the middle portion of the bypass connection, maintained at a
pressure of 0.5 bars (motor protection pressure). Thus, the accumulator
is not really put under pressure and is in no way dangerous;

[0138] Conversely, if the bypass valve 50 is in position II (assisted
mode), zero pressure is applied to the hydraulic chamber 761. The
accumulator valve is placed in position I, i.e. the accumulator is
connected to the transmission duct 54.

[0139] As a result of the connection between the port D of the bypass
valve and the hydraulic control chamber 761, the accumulator valve and
the bypass valve are coupled together, and the position of the bypass
valve imposes its position on the accumulator valve.

[0140] Operation of the hydraulic transmission apparatus 22 is described
below.

[0141] The hydraulic transmission apparatus 22 is used by complying with
certain stages marked mainly by activation or deactivation actions
performed on the various valves. The sequence of going from the
unassisted mode to the assisted mode, and vice versa, is shown in FIG. 2.
Certain significant steps in this sequence are shown in FIGS. 3 to 5.

[0142] Sequencing of the various steps is controlled automatically by an
electronic control unit (ECU) that is not shown, on the basis of the
assistance activation request (or of the assistance deactivation request)
by the driver of the vehicle. The ECU is also suitable for taking certain
protective measures for protecting the hydraulic transmission apparatus
22, while certain actions are being taken by the driver, such as
gear-changing or braking, as described below.

[0143]FIG. 2 shows, in particular, and as a function of time, the
positions taken up by the first bypass valve 50, and by the first and
second pilot valves 21 and 23. Underneath those curves lies a curve
showing the variations in the cylinder capacity D24 of the main pump 24.

[0144] Time is plotted along the abscissa, with, in particular,
significant times t0 to t11. The timing diagram shows a fictitious
scenario for use of the apparatus 22, in which scenario, starting from
the unassisted mode, at a time to, an assistance activation instruction
is issued by the driver of the vehicle. An assistance preparation first
stage takes place from t0 to t4. As from time t4, assistance is active
until time t7. However, the scenario in FIG. 2 makes provision for a
momentary assistance declutching stage from time t5 to t6. Finally, at a
time t7, an assistance disengagement request is made by the driver, and
the hydraulic assistance apparatus goes from the assisted mode to the
unassisted mode from t7 to t11.

[0145] In this mode, the bypass valve is in position I, and the fluid
delivered by the booster pump 25 flows through the bypass connection 64
to return to the reservoir 52, thereby following a relatively short
circuit, without using the various valves of the apparatus 22 (except for
the bypass valve 50). The accumulator valve 76 is in position II. The
accumulator empties via the valve 62 of the bypass connection. The
activation valve 34, the pilot valves 68 and 72, and the pressure control
valve 36 are in position I. The pump protection pressure prevails in the
upstream portion of the bypass connection 64, and therefore in the pump
ducts, thereby making it possible to protect the main pump 24. Said main
pump is being driven by the engine 18, but is not delivering.

[0146] Since the pump protection pressure is low (10 bars), the power
consumption by the auxiliary pump or booster pump 25 remains very low.

[0147] The casing ducts 40A and 40B are connected to the middle portion
562 of the bypass duct, in which a pressure of 0.5 bars prevails. This
pressure is sufficient to guarantee that the pistons remain in the
retracted positions inside the cylinders (and is chosen for the purpose).

Pass to Assisted Mode

Activate the Bypass Valve

[0148] At time t0, the driver issues an assistance instruction for putting
the transmission of the vehicle in assisted mode, i.e. for activating the
auxiliary transmission 20.

[0149] After a brief interval, at time t1, the ECU activates the bypass
valve 50 and places it in position II.

[0150] The accumulator valve 76 reacts immediately and goes from position
II to position I. The accumulator is thus connected to the booster pump
via the boost duct and via the transmission duct 54. It fills and rapidly
reaches the pressure delivered by the booster pump. Conversely, the
casing ducts 40A, 40B empty into the reservoir 52, via the valve 60 and
via the valve 50.

[0151] The accumulator is full at time t2. The ECU then, at time t3,
triggers synchronization of the main pump 24, by progressively increasing
the cylinder capacity of the pump, to a target value at which the
cylinder capacity is stabilized. This target value is determined by the
ECU in such a manner that the pump drives the motors 26A and 26B at a
speed of rotation equal to the speed of rotation of the wheels of the
vehicle. The instant t3 is determined by the ECU either after a set lapse
of time after t2 (0.5 seconds), or by a pressure reached on a pressure
switch.

[0152] The pistons, which were previously retracted into the cylinders,
are then deployed from their cylinders at time t4, and placed in the
working position, i.e. in contact with the cam. This operation is
triggered by activating the second pilot valve 72 that passes to position
II. As a result, the boost pressure applies in the hydraulic chamber 361,
thereby causing the pressure control valve 36 to pass to position II. As
a result, the pressure applied in the port B of the activation valve 34,
and therefore in the motor ducts 30, 32 rises, and reaches the boost
pressure.

[0153] Under the effect of this pressure, and since, conversely, the
casing ducts 40A, 40B remain at zero pressure, the pistons extend from
their cylinders, thereby enabling the rotors of the motors to turn at the
same speed as the wheels, the delivery rate of the pump adapting to said
speed. At this stage, the motors do not, however, deliver any torque.

[0154] Simultaneously with the pistons being deployed out of the
cylinders, the casing ducts 40A, 40B that are connected to the middle
portion 562 of the bypass duct 56 remove the fluid from the internal
spaces of the motors 26A, 26B via the check valve 60, towards the
reservoir 52.

[0155] Advantageously, during this stage, the accumulator 74 is put in
line at the same time as the booster pump 25 so as to deliver the fluid
and so as to fill the motor ducts 30 and 32. The accumulator thus
facilitates and accelerates filling the motor ducts and bringing them up
to pressure, and thus makes it possible for the motors 26A, 26B to be
positively clutched quickly.

Activate the Assistance Motors (FIG. 5)

[0156] Either slightly after the step of synchronizing the pump, or
simultaneously as shown in FIG. 2, the assistance motors are activated by
placing the first pilot valve 68 in the second position II. This causes
the activation valve 34 to go to position II and the respective pressures
of the pump ducts 28A, 28B thus apply in the motor ducts 30, 32. Under
the effect of the pressure difference between these ducts, the motors 26A
and 26B are thus caused to operate and they drive the wheels 14A and 14B
which thus become driven wheels.

[0157] The delivery rate of the pump is then progressively increased, as
the speed of the vehicle increases.

[0158] During the assistance stage, the accumulator 74 is connected to the
transmission duct 54 and remains subjected to the boost pressure.

Temporarily Deactivate the Assistance

[0159] If, during an assistance stage, it is necessary, for example, to
brake or to change gear (on the motors 26A, 26B), the assistance
apparatus 22 is deactivated temporarily during this stage.

[0160] This operation is performed (see FIG. 2) from times t5 to t6,
during which period the second pilot valve 68 is placed temporarily in
position I (deactivated position). As a result, during this period, the
activation valve 34 also returns to position I, and thus the pressure
balances out between the motor ducts. The motors 26A and 26B then,
temporarily, no longer deliver any drive torque or any braking torque.

Return to Unassisted Mode

[0161] The return to unassisted mode takes place as follows:

[0162] At an instant t7, the driver of the vehicle transmits a
return-to-unassisted-mode instruction to the ECU. Said ECU progressively
reduces the delivery rate of the main pump 24, in order to reduce the
assistance pressure to the minimum (to 30 bars) so as to reduce any jolts
in the assistance motors.

[0163] Then, after a predetermined lapse of time, the motors 26A, 26B are
deactivated by causing the first pilot valve 68 to go back to position I,
thereby causing the activation valve 34 to go to position I. The cylinder
capacity of the pump is then maintained constant for a short lapse of
time (from times t8 to t9), and then the reduction in the delivery rate
of the pump is resumed from times t9 to t10, whereupon the pump returns
to zero delivery rate.

[0164] At this time t10, the second pilot valve 72 is deactivated, which
enables the fluid contained in the motor ducts to be removed towards the
reservoir 52, and enables the pressure in them to be caused to drop.

[0165] Then, the bypass valve 50 itself is deactivated at time t11. The
valves are then in the positions shown by FIG. 3. However, initially the
flows of fluid are totally different from the unassisted mode, in
particular because the accumulator is initially under pressure (at the
boost pressure).

[0166] The fluid delivered by the booster pump is, once again, directed
towards the bypass duct 56. In addition, deactivation of the valve 50
causes the accumulator valve 76 to pass immediately to position II. The
accumulator is then put into communication firstly with the casing ducts
40A, 40B via the duct 66, and secondly with the reservoir 52, via the
calibrated valve 62.

[0167] The flow-rate of fluid that can pass through said valve 62 is,
however, limited. Thus, when the accumulator 74 is put into communication
with the duct 66, most of the fluid that it contains is removed towards
the reservoir 52, but during the initial moments after the accumulator 74
and the duct 66 have been put into communication with each other, a
non-negligible pressure is established in these ducts. This pressure is
transmitted to the internal spaces of the motors 26A, 26B via the casing
ducts 40A, 40B. Thus, the accumulator being put into communication makes
it possible to accelerate retraction of the pistons into the cylinders.

[0168] At the end of these operations, the vehicle finds itself in
unassisted mode, and the wheels 14A and 14B can turn freely, as in the
initial situation.

[0169] It should be noted that it is also possible firstly to deactivate
the bypass valve 50, and then to deactivate the second pilot valve 72.
The choice of such a sequence facilitates rapid retraction of the
pistons.

[0170] The arrangement of the valve 34 is described below with reference
to FIGS. 6A and 6B.

[0171] This valve has a body 100 inside which a substantially cylindrical
bore 102 is arranged along an axis X. A slide 104 that is substantially
in the shape of a cylindrical segment is slidably received in the bore.
Six circumferential grooves G1-G6 are also formed in the bore; two wide
circumferential grooves H1-H2 are formed in the outside surface of the
slide.

[0172] The valve 34 has four upstream ports A, B, C, and D, two of which
(A and D) coincide in practice because they are interconnected via an
internal duct 106. Port A-D is connected to the grooves G1 and G6; port B
is connected to groove G2 via an internal duct, and port C is connected
to groove G4 via an internal duct.

[0173] The valve 34 has two downstream ports E and F. Port E is connected
to groove G5 via an internal duct, and port F is connected to groove G3
via an internal duct. The slide is designed to take up two positions I
and II.

[0174] In position I, i.e. in the unassisted position (FIG. 6A), the slide
104 is positioned on the same side as groove G1 (rather than on the same
side as groove G6 along the axis X). In this position, groove H1 puts
grooves G1 and G2 into communication with each other, and groove H2 puts
grooves G3, G4, and G5 into communication with one another.

[0175] In position II, i.e. in the assisted mode (FIG. 6B), the slide 104
is positioned on the same side as the groove G6. In this position, groove
H1 puts grooves G2 and G3 into communication with each other; groove H2
puts grooves G5 and G6 into communication with each other.

Patent applications by André Prigent, Saintines FR

Patent applications by Jean Heren, Margny Les Compiegne FR

Patent applications by Philippe Lucienne, Aumont En Halatte FR

Patent applications by POCLAIN HYDRAULICS INDUSTRIE

Patent applications in class With control means for structure storing work driving energy (e.g., accumulator, etc.)

Patent applications in all subclasses With control means for structure storing work driving energy (e.g., accumulator, etc.)